1. Field of the Invention
The invention relates to a method for operation of an indirect extrusion press and an indirect extrusion press.
2. Description of the Related Art
During indirect pressing of crude metal blocks, the forming procedure to produce the pressed product takes place with the formation of a shell, for example. The crude metal blocks may be made, for example, of copper, brass or corresponding alloys, and the shell is formed in order to avoid contaminants on the surface of the block to be formed from getting into the finished pressed product. In this connection, a tool head comprising a die plate is kept smaller in its diameter than the inside diameter of a block, to such an extent that a shell having a wall thickness of about 0.2 mm to 2.0 mm remains on the inner wall of the block holder, in each instance, as is also disclosed, for example, in EP 0 224 115 B1. The formation of a shell can also be correspondingly advantageous in the case of other materials, for example aluminum.
In this connection, a distinction should be made between direct and indirect pressing procedures, whereby in direct pressing, larger pressed products can generally be produced, with guidance of a pressing punch and of the metal to be formed in the same direction. In indirect pressing, in which the pressing punch is called an indirect punch and the material are guided in opposite directions, significantly lower friction forces generally occur, because the material does not need to be displaced relative to the block holder. In general, however, only smaller pressed products can be produced in indirect pressing, because the pressed product must be discharged through the indirect punch.
To reduce material tensions in the indirect punch, DE 101 31 901 A1 proposes screwing a clearing ring onto the indirect punch and relieving stress with a counter-nut. Alternatively, a wear plate and/or a die plate is attached by way of insertion bolts that are shrunk-fit into corresponding bores of the indirect punch.
After one or more pressing procedures, the shell that has formed as a result of pressing of the block material must generally be removed, in order to be able to implement operationally reliable pressing for subsequent pressing procedures. In known methods, in order to remove the shell, the latter is pulled out of the block holder together with the tool head, accompanied by great disassembly effort and assembly effort. Almost complete removal of the shell from the block holder, without remnant, however, is not possible in this way. Moreover, a remaining remnant of the shell has a detrimental effect on subsequent pressing procedures or on the operational reliability of subsequent pressing procedures. This detrimental effect results because the remaining remnant can lead, particularly during pressing, to undesirable block compression of the metal block or material block during the loading procedure that is intended for the subsequent pressing procedure. Furthermore, the remaining remnant of the shell can hinder secure introduction of a new tool head or of a cleaned or repaired tool head into the block holder. In particular, the tool head can become jammed on the remaining remnant.